Reproduction is a complex process regulated by many factors, including the ovarian steroids. Although this process is of obvious importance, it is not adequataly understood in any species. The future success of dealing clinically with the reproductive spectrum, namely infertility and explosive growth rates, depends in part, on a more perfect understanding of the factors controlling the reproductive process. The broad objective of this proposed study is to clarify the interaction of the ovarian steroids with their receptor systems and to determine how this interaction regulates the morphological and biological state of reproductive tract tissue. One of our major aims will be to continue our studies on the effect progesterone has on uteri and oviducts when chronically administered to estradiol-primed cats. This will be accomplished by correlating the plasma levels of estradiol and progesterone, as determined by radioimmunoassay, with alterations in the levels of cytosol and nuclear receptors for estradiol and progesterone, as determined by dextram coated charcoal and exchange assays. The biological response progesterone may induce in uteri and oviducts, in addition to alterations in subcellar compartmentalization of the steroid receptor systems, will be quantitated biochemically by monitoring key enzymes (those involved in glycogen metabolism) amd morphologically by obtaining light and electron micrographs. An additional aim will be to purify a specific uterine protein whose synthesis is induced by estradiol and release is stimulated by progesterone. Our goal is to determine the bioloigical function of this protein and to assess whether it can be as a marker protein to study the mechanism of hormone action at the molecular and genetic level. This study should provide important data in how progesterone controls a) the postovulatory regressive phase of autolysis in the oviduct, and b) the preimplantation progestational phase of the uterus. Additional insight should also be gained into how the uterus supports blastocyst development prior to implantation.